/Engine/Source/Runtime/Slate/Public/Framework/Application/SlateApplication.h
Gets whether or not a particular widget has the specified users focus, and if so the type of focus.
The optional will be set with the focus cause, if unset this widget doesn't have focus.
virtual [TOptional](API\Runtime\Core\IO\TOptional)< EFocusCause > HasUserFocus ( const [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< const [SWidget](API\Runtime\SlateCore\Widgets\SWidget) > Widget, int32 UserIndex ) const